In automation and sensor networks, there is a need to guarantee integrity of data to be transmitted between different systems. This may be done by protecting the data with a cryptographic checksum, such as a message authentication code, message integrity code or digital signature, for example. A key management process is needed for this purpose, which supplies the systems involved with the necessary security parameters.
Transferring data using messages in automation and sensor networks is often done by broadcast messages or multicast messages.
In a widely established key management method for broadcast messages or multicast messages, which is used, for example, with Wireless Local Area Network (WLAN) based on standard Institute of Electrical and Electronics Engineers (IEEE) 802.11, the user nodes are informed of the multicast key or broadcast key by the access point. This has the disadvantage that a user node that has been tampered with may impersonate the broadcast/multicast sender, e.g., the access point.
For a secure broadcast/multicast transmission method, it has therefore been proposed to change relatively frequently the key used for sending broadcast/multicast messages, and to make the key accessible to a receiver node only after a time delay. Once the key used by the sender is known to the receiver node, then the key is already no longer valid for sending.
Using what are known as hash chains is a known option for providing keys for multicast scenarios. In this case, a plurality of keys are calculated in advance, wherein one particular key may be used for one specific period, which may be limited in terms of time or on the basis of messages to be sent.
Time Efficient Stream Loss-tolerant Authentication (TESLA) is a multicast protocol based on hash chains. A variation of the TESLA protocol is explained in greater detail under μTESLA. In this case, a particular multicast sender manages its own hash chain. A receiver manages respective hash-chain data explicit to each multicast sender. Such a method is suitable for the situations in which a single multicast sender serves a multiplicity of receiver nodes.
Embedded systems, which have limited processing and memory capacity, are often used in automation and sensor network systems. The TESLA multicast protocol is unsuitable especially for these systems because the hash chain takes into account parameters for a multiplicity of senders, which may result in the embedded system rapidly reaching its physical limits.